Connectors are used in many different industries, including building construction and mechanical and electrical equipment manufacture, to align and secure components. Such connectors may interconnect two structural members to form a structural frame which can be used as a load-bearing member for such applications as bridges, buildings, mounts for equipment and containers like pressure vessels, and assemblies of electrical and mechanical systems. The structural members to be connected may have various geometries, including flat and curved plates, ribs, struts, beams, girders, and columns, and may be made of steel, reinforced concrete, or composites of plastic, wood, steel and other materials.
As frames are erected, the structural members are positioned, aligned, and secured to each other using connectors. Connectors are also used to attach non-structural members, which include walls, facade, and other non-load bearing members, to the structural members. For either use, the connectors offer temporary or permanent attachment as desired.
Input from at least five different specialists within the construction industry is required to create structural frames. Architects determine the general form of the structure; steel mills produce the structural members with various nominal sizes; structural design engineers determine and select the nominal sizes of the structural members and the types of connectors required to make the frames which will allow the architectural form to sustain its loads and deflections; fabricators detail the connectors selected by the engineers, cut the structural members to the correct size, make or obtain the components of the connectors, and attach the connectors to the structural members (typically away from the erection site); and erectors take the fabricated elements and assemble them into a structural frame at the erection site.
Most structures include beams, columns, and girders which are welded or bolted to other members at their ends or mid-sections using connectors. The design engineer may choose from a variety of connector types: simple (shear), semi-rigid (partial-moment), and rigid (full-moment). A simple connector can withstand shear loads. It allows rotation, so that little or no moment is transferred between connected elements through the connector. A rigid connector transfers both shear and moment loads between connected elements allowing no relative rotation between the members. The current practice is to use simple or rigid connectors; semi-rigid connectors are atypical. The engineer determines the size of the loads that each connector will bear and the allowable deflections and rotations allowed at each connector. Using that information and the appropriate structural design codes and practices, the engineer chooses suitable structural elements and connectors.
The fabricator or, more specifically, the detailer who works for the fabricator, uses the design information and knowledge of both the manufacturing capabilities of the fabrication shop and the abilities of the erectors to detail each connector. Typically, a connector includes a number of components. The connector detail allows the fabricator to attach (by a combination of one or more cutting, drilling, welding, and bolting operations) the plates and other components of the connector to the beams, columns, and girders to be connected. Thus, the fabricator attaches certain components of a connector to one structural member at the shop and away from the erection site. Other components of the same connector may either be attached to a second structural member at the shop or shipped loose.
At the erection site, final assembly requires the erectors to pre-position and align the joining members, temporarily secure the connectors, plumb the structure, and make the connections permanent. Erectors attach the separate components of the connectors, usually by welding, bolting, or both. Typically, the structural members will not fit together properly without on-site modification. Such modifications are required by tolerance build-up within the structure, improperly fabricated members, improperly erected portions of the frame, or a combination of these problems.
Because modifications are required on-site, the common practice is to detail connectors which allow a temporary connection. Such a connection allows the members of the structure to be moved with sledge hammers, prying devices, and guy lines. Typically, temporary connection requires the use of a drift pin. In some cases, the drift pin is temporarily removed when a third structural member is connected to two members which have already been temporarily connected. Removal of the drift pin places the structure in an unstable position. This can be especially hazardous because the erector may be sitting on or suspended by one of the temporarily connected members.
The frame structure is usually assembled one floor at a time, although other groups of members may be used. A portion of the frame is first erected by making temporary connections between the main members, usually the vertical columns and horizontal beams or girders that interconnect those columns, of the frame. After the temporary connections are complete, the structure is made plumb using guy lines and shims placed in the connections to shift the positions of the beams and columns. Once plumb to within required tolerances, usually about one inch per floor, the connectors are permanently bolted or welded.
Bolted connectors are preferred by most construction companies because bolting is more easily done than welding at the erection site. Numerous bolt holes must be aligned at each of the connectors to bolt the members together. If alignment is impossible, old holes are enlarged or new holes are drilled. The bolts are then inserted into the aligned bolt holes and nuts are used to tighten them. Care must be exercised when tightening the bolts. Overtightening may stress the bolts and cause them to fail; overly loose bolts will cause the connector to slip. In either case, the connector will not function as designed.
Although not preferred, welded connectors are used. Welding is most typically done off-site at the fabrication shop because off-site welding is far cheaper than on-site welding, which is for that reason avoided whenever possible. In some cases, however, especially when rigid connectors are required, welding is done on site. Careful preconditioning of the weld area is essential to weld a structure. In particular, preheating of the members to be connected is necessary when welding many types of steel members. The connected members must meet tight tolerances to assure proper weld strength and toughness. The process of welding also requires highly trained labor and transport of awkward equipment through an inhospitable environment.
The prior art has included connector assemblies designed to assist in the on-site bolting and welding processes. Most of these assemblies incorporate slip-in-place components. Although ingenious, such assemblies have not been successfully implemented in the construction industry. That failure is attributable to a variety of reasons.
In 1928, Reinhold patented (U.S. Pat. No. 1,662,438) a clip device for temporarily supporting structural members used in buildings preparatory to welding. That device is dangerous if the beam moves longitudinally. Moreover, lateral movement of the clip would risk injury to the erector.
Stromberg patented (U.S. Pat. No. 2,008,087) a slide-in-place assembly including a plate or tongue and a supporting socket in 1932. The components fit tightly; the assembly does not allow adjustment of the members. Therefore, it is nearly impossible to attach the large members within the tolerances involved in building construction. This is especially true because both ends of a member must be placed and seated simultaneously using the assembly. If play were introduced into the assembly, the connection would no longer be rigid.
In 1945, McIntosh patented (U.S. Pat. No. 2,374,550) a stepped joint for connecting structural framework such as beams, girders, and columns. That joint does not address the problem of securing the members without bolting or welding. The joint is also eccentric and irregular, which invites structural problems. Moreover, the energy required to cold form the tongue after insertion in the slot either limits the connecting members to thin gauges or demands large amounts of energy. The latter risks local damage and weakening of the connector and structure.
In a series of patents (U.S. Pat. Nos. 2,231,297; 2,540,408; 2,624,429; 3,097,729; 3,017,972; 3,022,871; 3,025,936) between 1941 and 1963, Saxe disclosed a connector applied well below the center of gravity of the connected member. This device was used for temporarily supporting structural members before welding. Such an application tends to make the connection unstable. Moreover, the original design lacked adjustment capability. Although a later version provided for longitudinal adjustment, the failure of that version to assure lateral straightness renders it unsuccessful.
In 1972, Patenaude patented (U.S. Pat. No. 3,685,866) a support socket and wedge combination connector. That connector lacked any type of adjustment, required lots of material to construct, and provided a complex configuration for only shear transfer. Recently, in 1980, Hawes patented (U.S. Pat. No. 4,220,419) an improved connector for continuous beam welded steel structures. The disclosed connector does not attach to the web of the beam and, accordingly, has shortcomings as a full moment connector. Finally, Mullin patented (U.S. Pat. No. 4,586,300) an apparatus including a slot and wedge in 1986. That apparatus can only be applied, however, in light, temporary construction.
To overcome the shortcomings of existing connector assemblies, a new connector is provided. An object of the present invention is to provide an improved connector which will simplify the construction process. Related objects are to (1) permit the components of the connector to be attached to the members to be connected in the fabrication shop, (2) allow connection of the members without requiring bolting or welding, (3) provide connector components which can be easily engaged with minimal effort or force, and (4) reduce the detrimental effects of poor tolerances on the erection process.
Another object is to provide a connector which is flexible and versatile. Related objects are to provide a connector which can carry shear alone, shear and a partial moment, or shear and a full moment; allows adjustment of the connector components; and will temporarily or permanently fix members together. It is still another object of the present invention to provide a connector which is self-centering and self-aligning.
An additional object is to improve the safety features of existing connectors. That object is achieved by designing the connector for location at one end or a midpoint of a member along its center of gravity. Such a design assures a stable connection and helps to avoid danger to erectors. A related object is to provide a connector which can be assembled without damage to or weakening of either the connector or the members to be connected.
Yet another object of the invention herein disclosed and claimed is to provide a connector which is sufficiently compatible with the members to be connected that any desired field welds are simply and easily formed. Further aims are to provide a connector which is strong, durable, and dependable; inexpensive to manufacture; relatively compact and simple in design; and can be used with members of varying proportions.